Banned in China: Nigeria has banned the movie because it "portrays Nigerians as gangsters and cannibals". There are some cannibalistic Nigerian gangsters in the film, but it never says all Nigerians are gangsters. Nigerian immigrants into South Africa are often poor and are blamed for an increase in crime. The cannibalism is actually inspired by the treatment of albinos in Tanzania.
Dueling Movies: With Avatar, both competing for the title of "Humans Are the Real Monsters: The Movie" And while not dueling in content, it was one of three films released in the fall/winter of 2009 with "Nine" in the title, causing a little confusion among the less attentive of moviegoers.
The South Africans participating in the vox populi segments didn't realize they were being filmed about space aliens. They were asked their opinion on Nigerian immigrants, and their comments were edited to make it seem like they're complaining about the prawns.
Obesanjo's "Holy shit!" reaction when Wikus shoots the gangster - actor Eugene Khumbanyiwa was not prepared for the strength of the air compressors that blew out the side of the shack.
Fan Nickname: Christopher's son is referred to as either "C.J." or "Oliver" in most works of fandom, despite having no apparent canon name. The DVD subtitles give his name as "Little C.J." The name Oliver can actually be considered canon, as it was mentioned in this post to Christopher's blog that he had two children, named Oliver and Sherry.
Network to the Rescue: The film's entire existence is this trope. Neill Blomkamp was Peter Jackson's choice to helm the Halo film. When the budget of that reached $145 million, the studios canned it. Jackson then went to Blomkamp and essentially said "Sorry that didn't work out, here's $30 million, go have fun." It also counts as a complete avoidance of Executive Meddling. Jackson knew exactly what Neill was capable of and wanted him to do whatever he wanted, knowing it would be awesome.
Reality Subtext: Comes from the quote "if they were from another country, maybe we would understand" in the first half. Maybe intentional, maybe not, but it's hard to deny. In May 2008, (black) South Africans rioted to expel Zimbabweans (primarily) as well as Malawians and Mozambicans from the country, or hack them to death with machetes—whichever. At least two people died and many more were injured. Thousands of people left the country, while others were deported, and there's still (as there has been for decades) an underlying nationalist sentiment. So yeah, no.
Originally, Blomkamp and Jackson were attempting to adapt Halo into a movie. When that fell through, they went with this instead.
Five different endings were shot. One of them was apparently so embarrassing neither Blomkamp nor Copley will say a thing about it, with Blomkamp stating, "No one will ever see that ending." The only thing known about it at this point was that Copley got very, very dirty in the process.
Word of God: The fluid? It's actually a nanite solution used for fixing things.